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Productive Habitats (productive + habitat)
Selected AbstractsWinter commingling of populations of migratory species can cause breeding range underpopulationOIKOS, Issue 12 2007Alexander M. Mills We build a model with large-scale demographic consequences for migratory species. The model operates where four elements co-occur, and we rely on empirical research using migratory birds to demonstrate them. First, breeding ranges have internal structure flowing from natal philopatry. Second, fecundity varies geographically. Third, populations of different breeding provenances commingle during winter. And fourth, a population-limiting carrying capacity operates during winter. In the absence of breeding season population-limitation, only the breeding population with maximum fecundity persists. Consequently, some potential breeding areas that offer suitable and productive habitat are bereft of breeding birds because of the interplay between the geographical fecundity gradient and the shared winter quarters. Where breeding season population-limitation also plays a role for at least one population, one (or more) breeding population becomes permanently depressed, resulting in a density well below the carrying capacity of the productive breeding habitat that is occupied. In either case, not all populations fare equally well, despite net positive breeding season productivity. Changes in winter carrying capacity, for example habitat degradation in winter quarters, can lead to uneven effects on geographically defined breeding populations, even though there has been no change in the circumstances of the breeding range. [source] What determines the relationship between plant diversity and habitat productivity?GLOBAL ECOLOGY, Issue 6 2008Martin Zobel ABSTRACT The relationship between biodiversity and habitat productivity has been a fundamental topic in ecology. Although the relationship between these parameters may exhibit different shapes, the unimodal shape has been frequently encountered. The decrease in diversity at high productivity has usually been attributed to competitive exclusion. We suggest that evolutionary history and dispersal limitation may be even more important in shaping the diversity,productivity relationship. On a global scale, unimodal diversity,productivity relationships dominate in temperate regions, whereas positive relationships are more common in the tropics. This difference can be accounted for by contrasting evolutionary history. Temperate regions have smaller species pools for productive habitats since these habitats have been scarce historically for speciation, while the opposite is true for the tropics. In addition, dispersal within a region may limit diversity either due to the lack of dispersal syndromes at low productivity or the low number of diaspores at high productivity. Thereafter, biotic interactions (competition and facilitation) can shape the relationship. All these processes can act independently or concurrently. We recommend that the common approach to examining empirical diversity,environmental relationships should start with the role of large-scale processes such as evolutionary history and dispersal limitation, followed by influences associated with ecological interactions. [source] Home range dynamics of the yellow-footed rock-wallaby (Petrogale xanthopus celeris) in central-western QueenslandAUSTRAL ECOLOGY, Issue 1 2009ANDY SHARP Abstract Analyses of the interspecific differences in macropod home range size suggest that habitat productivity exerts a greater influence on range size than does body mass. This relationship is also apparent within the rock-wallaby genus. Lim reported that yellow-footed rock-wallabies (Petrogale xanthopus xanthopus) inhabiting the semi-arid Flinders Ranges (South Australia) had a mean home range of 170 ha. While consistent with the hypothesis that species inhabiting less productive habitats will require larger ranges to fulfil their energetic requirements, the ranges reported by Lim were considerably larger than those observed for heavier sympatric macropods. The aim of the current study was to document the home range dynamics of P. x. celeris in central-western Queensland and undertake a comparison with those reported for their southern counterparts. Wallaby movements were monitored at Idalia National Park, between winter 1992 and winter 1994. Male foraging ranges (95% fixed kernel; 15.4 ha, SD = ±7.8 ha) were found to be significantly larger than those of female wallabies (11.3 ha, SD = ±4.9 ha). Because of varying distances to the wallabies' favoured foraging ground (i.e. an adjacent herb field), the direction in which the wallabies moved to forage also significantly affected range size. Mean home range size was estimated to be 23.5 ha (SD = ±15.2 ha; 95% fixed kernel) and 67.5 ha (SD = ±22.4 ha; 100% minimum convex polygon). The discrepancy between these two estimates resulted from the exclusion of locations, from the 95% kernel estimates, when the wallabies moved to a water source 1.5 km distant from the colony site. The observed foraging and home ranges approximated those that could be expected for a macropod inhabiting the semi-arid zone (i.e. 2.4 times larger-than-predicted from body mass alone). Possible reasons for the disparity between the current study and that of Lim are examined. [source] A long-term record of Nothofagus dominance in the southern Andes, ChileAUSTRAL ECOLOGY, Issue 1 2005William Pollmann Abstract The general model of regeneration dynamics in Nothofagus forests of southern South America could have value in community ecology if predictive relationships between disturbance history, functional traits and site attributes could be identified. Examined here is the proposal that on favourable sites shade-intolerant Nothofagus are likely not to survive in competition with shade-tolerant, broad-leaved evergreen taxa of temperate rain forests, and persistence, thus, is dependent on periodic coarse-scale disturbance. Comparison of stand dynamics of three old-growth Nothofagus forests at different elevations in the southern Andes, Chile where deciduous Nothofagus alpina dominates the upper canopy, and examination of the life history trade-offs of this variation were made. Stem density of all stems ,5.0 cm d.b.h. was 233,303 stems per hectare, and basal area was 123.9,171.0 m2ha,1. Maximum lifespan of N. alpina was found to be greater than ca 640 years, exceeding all previously reported ages for this species in the region. Forests had a stable canopy composition for this long-term, but some appeared to lack effective regeneration of N. alpina in recent years. Regeneration of N. alpina was generally greater in disturbed stands and higher elevation than in undisturbed stands and at lower elevation. Recruitment emerged to be strongly affected by competitive over- and understorey associates. There was a gradient of increasing dependence of N. alpina on disturbance towards the more productive end of the environment gradients, and hence less dependence of N. alpina on disturbance for its regeneration towards higher elevation. The study confirms that changes in forest composition may be explained by processes occurring in accordance with the predictions of the existing model of Nothofagus regeneration dynamics, providing stronger evidence specifically directed at mid-tolerant N. alpina, and by factoring out regeneration dynamics on favourable sites. Thus, for N. alpina, trait differences probably contribute to the competitive advantage over its associates in productive habitats, and may be linked to small-to-intermediate-sized disturbances which inevitably occur as older trees die, enabling N. alpina to persist in forests and therefore maintain species coexistence for the long-term. [source] | ||||||||||